The present invention relates to a control apparatus for directional lamps of a vehicle and particularly to a control apparatus which functions to indicate the turning direction of the vehicle and to indicate each disconnection of a front, rear and side directional lamps by the frequency change in periodic flashing of the directional lamps.
It is known well in the direction indicating system of an automotive vehicle that a group of front, rear and side directional lamps are mounted at respective front, rear and side portions of the vehicle as vehicle directional lamps and these lamps are energized periodically to flash upon requirement for the indication of vehicle turning direction. It is also known that the periodic flashing of the directional lamps is controlled by an electronic control apparatus designed to detect and indicate the disconnection of the lamps.
One of this system is disclosed in the prior art, U.S. Pat. No. 3,858,177, in which a control apparatus is provided to control the periodic flashing of the front and rear lamps. This control apparatus includes a capacitor which is charged and discharged alternately and a comparator which compares the voltage across the capacitor with a reference voltage to reverse the charge and discharge of the capacitor. Since the reference voltage is changed from one to the other value upon disconnection of the front or rear directional lamp and these lamps are energized during either the charge or discharge of the capacitor, the flashing frequency of the directional lamps is changed upon lamp disconnection for the disconnection indicating purpose. It should be noticed that the lamp disconnection indication is required in relation not only to the front and rear directional lamps but also to the side directional lamp. It should be noticed further that, since the voltage across the capacitor in the control apparatus changes exponentially, a small change in the reference voltage results in a large change in the flashing frequency of the directional lamps.